// sanjiao.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

int main(int argc, char* argv[])
{double a,b,c,p,s;
scanf("%lf %lf %lf",&a,&b,&c);
p=(a+b+c)/2;
s=p*(p-a)*(p-b)*(p-c);
	printf("%.2lf",s);
	return 0;
}

